Ancient teeth hint at canoodling between early human relatives

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NEW YORK (AP) — An analysis of ancient teeth is giving scientists a rare peek into interactions between human relatives hundreds of thousands of years ago that have left a lasting imprint on our species.

A new study reveals genetic clues about a human ancestor called Homo erectus. H. erectus arose in Africa about 2 million years ago and spread to other parts of the globe, including Asia and possibly Europe.

Scientists have found remains from this early human in countries including Indonesia, Spain, China and Georgia. But genes and proteins don't preserve well so information about the early humans' internal makeup has proved elusive.

In a new work, researchers siphoned ancient enamel proteins from H. erectus teeth belonging to five men and one woman that were recovered across several locations in China to learn how these early humans may have mingled.

The 400,000-year-old teeth all had two key mutations in a protein found in tooth enamel. One mutation hasn't been observed before and could be a unique calling card belonging to East Asian members of H. erectus.

The second, though, was more complex. Scientists identified a variant that's also present in a small fraction of modern humans — as well as one of our extinct cousins called Denisovans.

That told scientists that H. erectus could have mated with and passed their genes to Denisovans in the past. But how did it get to us? Scientists think that may have happened later when our ancestors intermingled with Denisovans.

“This traces who we are now back to our ancestors in a really cool and exciting way, using new methods,” said paleoanthropologist Ryan McRae with the Smithsonian National Museum of Natural History, who was not involved with the new research.

The exact relationships between all these early human relatives are still a bit murky. It could be that H. erectus is actually just an ancestor to the Denisovans, who inherited those genes over time, McRae said.

It's a tough puzzle to detangle with extremely limited data. Finding more fossils and testing the limited evidence for remnants of DNA can help firm up the human evolutionary story.

“We really need to get more DNA” and bits of H. erectus to figure out how this predecessor “is exactly related to other humans,” said study author Qiaomei Fu with the Institute of Vertebrate Paleontology and Paleoanthropology in China.

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